9 Answers
9

The easiest ways to kill people wielding riot shields (not including using kill streak rewards) are to stick them with semtex, shoot them in the feet, or throw a grenade behind them (hopefully right under them if possible).

Another way is to flash them or use a concussion grenade (I prefer concussion, because they physically can't turn to face you, whereas they can fluke it with a flash) and flank them and shoot their sides/back (or knife them).

Alternatively, wait until they lift the shield and shoot them (although I assume you've been trying this and it's why you've been getting killed).

(When I figure out more methods, I'll edit this, but I haven't really come across too many riot shielders yet).

9-Bang (Flashbang) or concussion grenade them straight in the face if you have Blast Shield and run into their sides or back, and then either put a knife or a bullet or two into them. If they are in a confined space, then first throw the flash/concussion, then rush in.

If they are running, it means they are standing, shoot them at their feet. If they crouch, try to flank them, still shooting. The "still shooting" part is important. Keep them nailed to blur their vision.

Throw a nade behind them. Even if it falls far, this will make most fear and turn in the nade's direction, which leaves you with their back. You know what to do..

If they are crouching and have their backs on a wall or a corner, then either SMAW them or lob a nade behind them.

Alternatively, if you are wielding a Riot Shield yourself, too, go charge them - may the faster flanker win!

You have to have really accurate shots to kill a riot shield soldier. One tricky way (which may be easy to most of you) is to aim for their shooting arm, and it is also good if you put C4 where you know they will be walking.

The way I prefer to do it is to throw a flash bang at them and when they're flashed run behind them an knife them. In close corners I don't believe it's possible to have a real strategy if it's just you versus them. Your best bet is to run to a more open place.

Hmmm this is really not very explanatory... I mean, could you formulate a better answer (like the one how is the accepted one)? In my opinion, this is more of a comment (or an edit to the accepted answer).
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MichelDec 14 '12 at 11:06